Semiconductor substrate cutting method

ABSTRACT

A semiconductor substrate cutting method which can efficiently cut a semiconductor substrate having a front face formed with a functional device together with a die bonding resin layer is provided.  
     A wafer  11  having a front face  3  formed with a functional device  15  is irradiated with laser light L while positioning a light-converging point P within the wafer  11  with the rear face  17  of the wafer  11  acting as a laser light incident face, so as to generate multiphoton absorption, thereby forming a starting point region for cutting  8  due to a molten processed region  13  within the wafer  11  along a line along which the substrate should be cut  5 . Consequently, a fracture can be generated from the starting point region for cutting  8  naturally or with a relatively small force, so as to reach the front face  3  and rear face  17 . Therefore, when an expansion film  21  is attached to the rear face  17  of the wafer  11  by way of a die bonding resin layer  23  after forming the starting point region for cutting  8  and then expanded, the wafer  11  and die bonding resin layer  23  can be cut along the line along which the substrate should be cut  5.

TECHNICAL FIELD

The present invention relates to a semiconductor substrate cuttingmethod used for cutting a semiconductor substrate having a front faceformed with a functional device in a process of making a semiconductordevice and the like.

BACKGROUND ART

As a conventional technique of this kind, Patent Document 1 and PatentDocument 2 disclose the following technique. First, an adhesive sheet isattached to the rear face of a semiconductor wafer by way of a diebonding resin, and a blade cuts the semiconductor wafer while thesemiconductor wafer is held on the adhesive sheet, so as to yieldsemiconductor chips. When picking up the semiconductor chips on theadhesive sheet, the die bonding resin is peeled off together with theindividual semiconductor chips. This can bond each semiconductor chiponto a lead frame while saving steps such as the step of applying anadhesive to the rear face of the semiconductor chip.

Patent Document 1: Japanese Patent Application Laid-Open No. 2002-158276

Patent Document 2: Japanese Patent Application Laid-Open No. 2000-104040

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, when cutting the semiconductor wafer held on the adhesive sheetwith a blade, it is necessary for techniques such as the one mentionedabove to reliably cut the die bonding resin layer existing between thesemiconductor wafer and the adhesive sheet without cutting the adhesivesheet. Therefore, care must be taken in particular when cutting thesemiconductor wafer with a blade in such a case.

In view of such circumstances, it is an object of the present inventionto provide a semiconductor substrate cutting method which canefficiently cut a semiconductor substrate having a front face formedwith a functional device together with a die bonding resin layer.

MEANS FOR SOLVING PROBLEM

For achieving the above-mentioned object, the present invention providesa semiconductor substrate cutting method for cutting a semiconductorsubstrate having a front face formed with a functional device along aline along which the substrate should be cut, the method comprising thesteps of irradiating the semiconductor substrate with laser light whilepositioning a light-converging point within the semiconductor substratewith a rear face of the semiconductor substrate acting as a laser lightincident face, so as to form a modified region, and causing the modifiedregion to form a starting point region for cutting along the line alongwhich the substrate should be cut inside by a predetermined distancefrom the laser light incident face; and attaching an expandable holdingmember to a rear face of the semiconductor substrate by way of a diebonding resin layer after forming the starting point region for cutting;and cutting the semiconductor substrate and die bonding resin layeralong the line along which the substrate should be cut by expanding theholding member after attaching the holding member.

A semiconductor substrate having a front face formed with a functionaldevice is an object to be processed in this semiconductor substratecutting method. Such a semiconductor substrate is irradiated with laserlight while positioning a light-converging point within thesemiconductor substrate with the rear face of the semiconductorsubstrate acting as a laser light incident face, whereby multiphotonabsorption or optical absorption equivalent thereto, for example, isgenerated, and a starting point region for cutting due to the modifiedregion is formed within the semiconductor substrate along the line alongwhich the substrate should be cut. Here, the rear face of thesemiconductor substrate is employed as the laser light incident face,since there is a fear of the functional device restraining laser lightfrom entering when the front face is used as the laser light incidentface. When the starting point region for cutting is formed within thesemiconductor substrate as such, a fracture can be generated from thestarting point region for cutting acting as a start point naturally orwith a relatively small force applied thereto, so as to reach the frontface and rear face of the semiconductor substrate. Therefore, after thestarting point region for cutting is formed, an expandable holdingmember is attached to the rear face of the semiconductor substrate byway of a die bonding resin layer and then is expanded, whereby cutsurfaces of the semiconductor substrate cut along the line along whichthe substrate should be cut are released from their close contact stateas the holding member expands. This also cuts the die bonding resinlayer existing between the semiconductor substrate and holding memberalong the line along which the substrate should be cut. Hence, thesemiconductor substrate and die bonding resin layer can be cut along theline along which the substrate should be cut much more efficiently thanin the case cut with a blade. Also, since the cut surfaces of thesemiconductor substrate cut along the line along which the substrateshould be cut are initially in close contact with each other, the cutindividual pieces of the semiconductor substrate and the cut individualpieces of the die bonding resin layer have substantially the same outershape, whereby the die bonding resin can be prevented from protrudingfrom the cut surface of each piece of the semiconductor substrate.

Here, the starting point region for cutting refers to a region to becomea cut start point when the semiconductor substrate is cut. The startingpoint region for cutting may be formed when a modified region is formedcontinuously or intermittently. The functional device refers tosemiconductor active layers formed by crystal growth, light-receivingdevices such as photodiodes, light-emitting devices such as laserdiodes, and circuit devices formed as circuits, for example.

Preferably, the method further comprises the step of grinding the rearface of the semiconductor substrate such that the semiconductorsubstrate attains a predetermined thickness before forming the startingpoint region for cutting. When the rear face of the semiconductorsubstrate is thus ground beforehand such that the semiconductorsubstrate attains a predetermined thickness, the semiconductor substrateand die bonding resin layer can be cut more accurately along the linealong which the substrate should be cut. Here, the grinding encompassescutting, polishing, chemical etching, etc.

The modified region may include a molten processed region. When theobject to be processed is a semiconductor substrate, a molten processedregion may be formed upon irradiation with laser light. Since thismolten processed region is an example of the above-mentioned modifiedregion, the semiconductor substrate can be cut easily in this case aswell, whereby the semiconductor substrate and die bonding resin layercan be cut efficiently along the line along which the substrate shouldbe cut.

The modified region may include a molten processed region and a minutevoid positioned on the opposite side of the molten processed region fromthe laser light incident face. When the object to be processed is asemiconductor substrate, the molten processed region and minute void maybe formed upon irradiation with laser light. Since the molten processedregion and minute void constitute an example of the modified region, thesemiconductor substrate can easily be cut in this case as well, wherebythe semiconductor substrate and die bonding resin layer can efficientlybe cut along the line along which the substrate should be cut.

When forming the starting point region for cutting in the semiconductorsubstrate cutting method in accordance with the present inventionexplained in the foregoing, a fracture may be allowed to reach the frontface of the semiconductor substrate from the starting point region forcutting acting as a start point, the rear face of the semiconductor fromthe starting point region for cutting acting as a start point, or thefront face and rear face of the semiconductor substrate from thestarting point region for cutting acting as a start point.

Preferably, the method further comprises the step of heating the diebonding resin layer before the step of cutting the semiconductorsubstrate and die bonding resin layer along the line along which thesubstrate should be cut by expanding the holding member. When the diebonding resin layer is heated before expanding the holding member, thedie bonding resin layer can be cut more accurately and easily along theline along which the substrate should be cut by expanding the holdingmember.

EFFECT OF THE INVENTION

In the present invention, a semiconductor substrate having a front faceformed with a functional device can efficiently be cut together with adie bonding resin layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a semiconductor substrate during laserprocessing by the laser processing method in accordance with anembodiment of the present invention;

FIG. 2 is a sectional view of the semiconductor substrate taken alongthe line II-II of FIG. 1;

FIG. 3 is a plan view of the semiconductor substrate after laserprocessing by the laser processing method in accordance with theembodiment;

FIG. 4 is a sectional view of the semiconductor substrate taken alongthe line IV-IV of FIG. 3;

FIG. 5 is a sectional view of the semiconductor substrate taken alongthe line V-V of FIG. 3;

FIG. 6 is a plan view of the semiconductor substrate cut by the laserprocessing method in accordance with the embodiment;

FIG. 7 is a view showing a photograph of a cut section of a siliconwafer formed with a molten processed region by the laser processingmethod in accordance with the embodiment;

FIG. 8 is a graph showing relationships between the laser lightwavelength and the internal transmittance of a silicon substrate in thelaser processing method in accordance with the embodiment;

FIG. 9 is a sectional view of the semiconductor substrate formed with amolten processed region and a minute void by the laser processing methodin accordance with the embodiment;

FIG. 10 is a sectional view for explaining a principle by which themolten processed region and minute void are formed by the laserprocessing method in accordance with the embodiment;

FIG. 11 is a view showing photographs of a cut section of a siliconwafer formed with molten processed regions and minute voids by the laserprocessing method in accordance with this embodiment;

FIG. 12 is a plan view of a silicon wafer to become an object to beprocessed in the semiconductor substrate cutting method in accordancewith the embodiment;

FIG. 13 is a schematic view for explaining the semiconductor substratecutting method in accordance with the embodiment, in which (a), (b), and(c) illustrate respective states where a protective film is attached tothe silicon wafer, the silicon wafer is thinned, and the protective filmis irradiated with UV rays;

FIG. 14 is a schematic view for explaining the semiconductor substratecutting method in accordance with the embodiment, in which (a), (b), and(c) illustrate respective states where the silicon wafer and protectivefilm are secured onto a mounting table, the silicon wafer is irradiatedwith laser light, and a starting point region for cutting is formedwithin the silicon wafer;

FIG. 15 is a schematic view for explaining the semiconductor substratecutting method in accordance with the embodiment, in which (a), (b), and(c) illustrate respective states where a die bonding resin bearing filmis attached to the silicon wafer, the protective film is peeled off fromthe silicon wafer, and the expansion film is irradiated with Lw rays;

FIG. 16 is a schematic view for explaining the semiconductor substratecutting method in accordance with the embodiment, in which (a), (b), and(c) illustrate respective states where the expansion film is expanded,semiconductor chips are picked up together with cut pieces of a diebonding resin layer, and the semiconductor chip is joined to a leadframe by way of the die bonding resin layer;

FIG. 17 is a schematic view showing the relationship between the siliconwafer and the starting point region for cutting in the semiconductorsubstrate cutting method in accordance with the embodiment, in which (a)and (b) illustrate respective states where no fracture is generated fromthe starting point region for cutting acting as a start point, and afracture from the starting point region for cutting acting as a startpoint reaches the front face and rear face of the silicon wafer;

FIG. 18 is a schematic view showing the relationship between the siliconwafer and the starting point region for cutting in the semiconductorsubstrate cutting method in accordance with the embodiment, in which (a)and (b) illustrate respective states where a fracture from the startingpoint region for cutting acting as a start point reaches the front faceof the silicon wafer, and a fracture from the starting point region forcutting acting as a start point reaches the rear face of the siliconwafer;

FIG. 19 is a schematic view for explaining a specific example of thesemiconductor substrate cutting method in accordance with theembodiment, in which (a), (b), and (c) illustrate respective stateswhere the silicon wafer and protective film are secured onto a mountingtable, the silicon wafer is irradiated with laser light, and thestarting point region for cutting is formed within the silicon wafer;

FIG. 20 is a schematic view for explaining the specific example of thesemiconductor substrate cutting method in accordance with theembodiment, in which (a), (b), and (c) illustrate respective stateswhere a die bonding resin layer is secured to the silicon wafer, the diebonding resin layer is irradiated with laser light, and the die bondingresin layer is formed with a modified region;

FIG. 21 is a schematic view for explaining the specific example of thesemiconductor substrate cutting method in accordance with theembodiment, in which (a), (b), and (c) illustrate respective stateswhere an expansion film is attached to the die bonding layer by way ofan adhesive layer, the protective film is peeled off from the siliconwafer, and the expansion film is expanded;

FIG. 22 is a schematic view for explaining another specific example ofthe semiconductor substrate cutting method in accordance with theembodiment, in which (a), (b), and (c) illustrate respective stateswhere a die bonding resin bearing film is attached to the silicon wafer,the die bonding resin layer is irradiated with laser light, and the diebonding resin is formed with a modified region; and

FIG. 23 is a view for explaining another specific example of thesemiconductor substrate cutting method in accordance with theembodiment, in which (a), (b), and (c) illustrate respective stateswhere the silicon wafer is removed from a mounting table of a laserprocessing apparatus, the protective film is peeled off from the siliconwafer, and the expansion film is expanded.

Explanations of Numerals

1 . . . semiconductor substrate; 3 . . . front face; 5 . . . line alongwhich the semiconductor substrate should be cut; 7 . . . modifiedregion; 8 . . . starting point region for cutting; 11 . . . siliconwafer (semiconductor substrate); 13 . . . molten processed region; 14 .. . minute void; 15 . . . functional device; 17 . . . rear face (laserlight incident face); 21 . . . expansion film (holding member); 23 . . .die bonding resin layer; 28 . . . fracture; L . . . laser light; P . . .light-converging point.

BEST MODES FOR CARRYING OUT THE INVENTION

In the following, a preferred embodiment of the semiconductor substratecutting method in accordance with the present invention will beexplained in detail with reference to the drawings. This embodimentutilizes a phenomenon of multiphoton absorption for forming a modifiedregion within a semiconductor substrate. Therefore, a laser processingmethod for forming a modified region due to multiphoton absorption willbe explained at first.

A material becomes optically transparent if its absorption bandgap E_(G)is greater than a photon energy hν. Hence, the condition under whichabsorption occurs in the material is hν>E_(G). However, even whenoptically transparent, the material yields absorption under thecondition of nhν>E_(G)(n=2, 3, 4, . . .) if the intensity of laser lightis very high. This phenomenon is known as multiphoton absorption. In thecase of pulse waves, the intensity of laser light is determined by thepeak power density (W/cm²) of laser light at a light-converging pointthereof. The multiphoton absorption occurs, for example, at a peak powerdensity (W/cm²) of 1×10⁸ (W/cm²) or higher. The peak power density isdetermined by (energy per pulse of laser light at the light-convergingpoint)/(laser light beam spot cross-sectional area×pulse width). In thecase of a continuous wave, the intensity of laser light is determined bythe electric field strength (W/cm²) of laser light at thelight-converging point.

The laser processing method in accordance with an embodiment of thepresent invention utilizing such multiphoton absorption will beexplained with reference to FIGS. 1 to 6. As shown in FIG. 1, asemiconductor substrate 1 has a front face 3 provided with a line alongwhich the substrate should be cut 5 for cutting the semiconductorsubstrate 1. The line along which the substrate should be cut 5 is avirtual line extending straight. In the laser processing method inaccordance with this embodiment, the semiconductor substrate 1 isirradiated with laser light L while a light-converging point P ispositioned within the semiconductor substrate 1 under a condition wheremultipboton absorption occurs. The light-converging point P is alocation where the laser light L converges. The line along which thesubstrate should be cut 5 may be either straight or curved, and is notlimited to the virtual line, but may be a line actually drawn on thesemiconductor substrate 1.

Then, the laser light L is relatively moved along the line along whichthe substrate should be cut 5 (i.e., in the direction of arrow A in FIG.1), so as to move the light-converging point P along the line alongwhich the substrate should be cut 5. This forms a modified region 7within the semiconductor substrate 1 along the line along which thesubstrate should be cut 5 as shown in FIGS. 3 to 5, and this modifiedregion 7 becomes a starting point region for cutting 8. The laserprocessing method of this embodiment forms no modified region 7 bycausing the semiconductor substrate 1 to absorb the laser light L uponheating the semiconductor substrate 1. Instead, the laser light L istransmitted through the semiconductor substrate 1, so as to generatemultiphoton absorption within the semiconductor substrate 1, therebyforming the modified region 7. Hence, the front face 3 of thesemiconductor substrate 1 hardly absorbs the laser light L, and thusdoes not melt.

When the starting point region for cutting 8 is formed within thesemiconductor substrate 1, a fracture is likely to occur from thestarting point region for cutting 8 acting as a start point, whereby thesemiconductor substrate 1 can be cut as shown in FIG. 6 with arelatively small force. Therefore, the semiconductor substrate 1 can becut with a high accuracy without generating unnecessary fractures in thefront face 3 of the semiconductor substrate 1.

There seem to be the following two cases in the cutting of thesemiconductor substrate 1 from the starting point region for cutting 8acting as a start point. The first case is where, after forming thestarting point region for cutting 8, an artificial force is applied tothe semiconductor substrate 1, so that the semiconductor substrate 1fractures from the starting point region for cutting 8 acting as a startpoint, whereby the semiconductor substrate 1 is cut. This is the cuttingin the case where the semiconductor substrate 1 has a large thickness,for example. The application of an artificial force encompassesapplication of bending stress and shearing stress along the startingpoint region for cutting 8 of the semiconductor substrate 1, andexertion of a temperature difference upon the semiconductor substrate 1to generate thermal stress, for example. The other case is where thestarting point region for cutting 8 is formed, so that the semiconductorsubstrate 1 is naturally fractured in a cross-sectional direction(thickness direction) of the semiconductor substrate 1 from the startingpoint region for cutting 8 acting as a start point, whereby thesemiconductor substrate 1 is cut. This is enabled, for example, byforming the starting point region for cutting 8 by a single row ofmodified regions 7 when the semiconductor substrate 1 has a smallthickness, and by a plurality of rows of modified regions 7 aligned inthe thickness direction when the semiconductor substrate 1 has a largethickness. Even in the case of natural fracturing, fractures do notextend to the front face 3 at a location not formed with the startingpoint region for cutting 8 in the part to cut, whereby only the partcorresponding to the location formed with the starting point region forcutting 8 can be fractured. Thus, fracturing can be regulated well. Sucha fracturing method with favorable controllability is quite effective,since the semiconductor substrate 1 such as a silicon wafer has recentlybeen apt to become thinner.

The modified region formed by multiphoton absorption in this embodimentincludes the following cases (1) and (2):

(1) Case where the Modified Region is a Molten Processed Region

A semiconductor material is irradiated with laser light while alight-converging point is positioned therewithin under a condition withan electric field intensity of at least 1×10⁸ (W/cm²) at thelight-converging point and a pulse width of 1 μs or less. As aconsequence, the inside of the semiconductor substrate is locally heatedby multiphoton absorption. This heating forms a molten processed regionwithin the semiconductor substrate. The molten processed region refersto a region once melted and then re-solidified, a region just in amelted state, or a region in the process of re-solidifying from itsmelted state, and may also be defined as a phase-changed region or aregion having changed its crystal structure. The molten processed regionmay also be regarded as a region in which a certain structure haschanged into another structure in monocrystal, amorphous, andpolycrystal structures. Namely, it refers to a region in which amonocrystal structure has changed into an amorphous structure, a regionin which a monocrystal structure has changed into a polycrystalstructure, and a region in which a monocrystal structure has changedinto a structure including an amorphous structure and a polycrystalstructure, for example. When the semiconductor substrate has a siliconmonocrystal structure, the molten processed region is an amorphoussilicon structure, for example. The upper limit of electric fieldintensity is 1×10¹² (W/cm²), for example. The pulse width is preferably1 ns to 200 ns, for example.

By an experiment, the inventors have verified that a molten processedregion is formed within a silicon wafer which is an example ofsemiconductor substrate. Conditions for the experiment are as follows:

(A) Semiconductor Substrate: silicon wafer (having a thickness of 350 μmand an outer diameter of 4 inches)

(B) Laser

-   -   Light source: semiconductor laser pumping Nd:YAG laser    -   Wavelength: 1064 nm    -   Laser light spot cross-sectional area: 3.14×10⁻⁸ cm²    -   Oscillation mode: Q-switch pulse    -   Repetition frequency: 100 kHz    -   Pulse width: 30 ns    -   Output: 20 μJ/pulse    -   Laser light quality: TEM₀₀    -   Polarization characteristic: linear polarization

(C) Light-converging lens

-   -   Magnification: +50    -   N. A.: 0.55    -   Transmittance with respect to laser light wavelength: 60%

(D) Moving speed of a mounting table mounting the semiconductorsubstrate: 100 mm/sec

FIG. 7 is a view showing a photograph of a cut section in a part of asilicon wafer cut by laser processing under the above-mentionedconditions. A molten processed region 13 is formed within a siliconwafer 11. The size of the molten processed region 13 formed under theabove-mentioned conditions is about 100 μm in the thickness direction.

The fact that the molten processed region 13 is formed by multiphotonabsorption will now be explained. FIG. 8 is a graph showingrelationships between the wavelength of laser light and thetransmittance within the silicon substrate. Here, respective reflectingcomponents on the front face side and rear face side of the siliconsubstrate are eliminated, whereby only the transmittance therewithin isrepresented. The above-mentioned relationships are shown in the caseswhere the thickness t of the silicon substrate is 50 μm, 100 μm, 200 μm,500 μm, and 1000 μm, respectively.

For example, it is seen that laser light is transmitted through thesilicon substrate by at least 80% at 1064 nm, where the wavelength ofNd:YAG laser is located, when the silicon substrate has a thickness of500 μm or less. Since the silicon wafer 11 shown in FIG. 7 has athickness of 350 μm, the molten processed region 13 due to multiphotonabsorption is formed near the center of the silicon wafer, i.e., at apart separated from the front face by 175 am. The transmittance in thiscase is 90% or greater with reference to a silicon wafer having athickness of 200 μm, whereby the laser light is absorbed within thesilicon wafer 11 only slightly and is substantially transmittedtherethrough. This means that the molten processed region 13 is notformed by laser light absorption within the silicon wafer 11 (i.e., notformed upon usual heating with laser light), but by multiphotonabsorption. The forming of a molten processed region by multiphotonabsorption is described, for example, in “Processing CharacteristicEvaluation of Silicon by Picosecond Pulse Laser”, Preprints of theNational Meeting of Japan Welding Society, No. 66 (April 2000), pp.72-73.

Here, a fracture is generated in the cross-sectional direction whileusing a molten processed region as a start point, whereby the siliconwafer is cut when the fracture reaches the front face and rear face ofthe silicon wafer. The fracture reaching the front face and rear face ofthe silicon wafer may grow naturally or grow as a force is applied tothe silicon wafer. The fracture may naturally grow from the startingpoint region for cutting to the front face and rear face of the siliconwafer in any of the cases where the fracture grows from the moltenprocessed region in a melted state and where the fracture grows from themolten processed region in the process of re-solidifying from the meltedstate. In any of these cases, the molten processed region is formed onlywithin the silicon wafer in the cut section after cutting, the moltenprocessed region is formed only therewithin as shown in FIG. 7. When amolten processed region is formed within the semiconductor substrate assuch, unnecessary fractures deviating from a line along which thesubstrate should be cut are hard to occur at the time of fracturing,which makes it easier to control the fracturing.

(2) Case where the Modified Region is Constituted by a Molten ProcessedRegion and a Minute Void

A semiconductor substrate is irradiated with laser light while alight-converging point is positioned therewithin under a condition withan electric field intensity of at least 1×10⁸ (W/cm²) at thelight-converging point and a pulse width of 1 μs or less. This may forma molten processed region and a minute void within the semiconductorsubstrate. When the laser light L is incident on the semiconductorsubstrate 1 from the front face 3 side as shown in FIG. 9, a minute void14 is formed on the rear face 17 side of the molten processed region 13.Though the molten processed region 13 and the minute void 14 are formedso as to be separated from each other in FIG. 9, there is a case wherethe molten processed region 13 and the minute void 14 are formedcontinuously with each other. Namely, when the molten processed regionand minute void are formed as a pair by multiphoton absorption, theminute void is formed on the opposite side of the molten processedregion from the laser light incident face in the semiconductorsubstrate. The upper limit for the electric field intensity is 1×10¹²(W/cm²), for example. The pulse width is preferably 1 ns to 200 ns, forexample.

A principle by which minute voids 14 are formed so as to correspond torespective molten processed regions 13 when the laser light L istransmitted through the semiconductor substrate 1, so as to generatemultiphoton absorption, thereby forming the molten processed regions 13is not totally clear. Here, two hypotheses presumed by the inventorsconcerning the principle by which the molten processed regions 13 andminute voids 14 are formed in pairs will be explained.

The following is the first hypothesis presumed by the inventors. Whenthe semiconductor substrate 1 is irradiated with laser light L while itsfocal point is positioned at a light-converging point P within thesemiconductor substrate 1 as shown in FIG. 10, a molten processed region13 is formed near the light-converging point P. Conventionally, lightcomponents (L4 and L5 in FIG. 10) in the center part of the laser lightL emitted from a laser light source have been used as the laser light L.This aims at employing the center part of the Gaussian distribution oflaser light L. In order to restrain the laser light L from affecting thefront face 3 of the semiconductor substrate 1, the inventors havedecided to widen the laser light L. As a technique therefor, the laserlight L emitted from the laser light source is expanded by apredetermined optical system, so as to widen skirts of the Gaussiandistribution, thereby relatively increasing the laser intensity of lightcomponents (L1 to L3 and L6 to L8 in FIG. 10) in marginal parts of thelaser light. When thus expanded laser light L is transmitted through thesemiconductor substrate 1, a molten processed region 13 is formed nearthe light-converging point P as explained above, and a minute void 14 isformed at a part corresponding to the molten processed region 13.Namely, the molten processed region 13 and minute void 14 are formed atrespective positions along the optical axis (the dash-single-dot line inFIG. 10) of the laser light. The position where the minute void 14 isformed corresponds to a part where the light components (L1 to L3 and L6to L8 in FIG. 10) in marginal parts of the laser light L aretheoretically converged. It seems to be because of the sphericalaberration of a lens converging the laser light L that light components(L4 and L5 in FIG. 10) in the center part of the laser light areconverged at a position different from positions where the lightcomponents (L1 to L3 and L6 to L8 in FIG. 10) in marginal parts of thelaser light L are converged as such in terms of the thickness directionof the semiconductor substrate 1. The first hypothesis presumed by theinventors lies in that this difference in light-converging positionsexerts some influences.

The following is the second hypothesis presumed by the inventors. Thepart where the light components (L1 to L3 and L6 to L8 in FIG. 10) inmarginal parts of the laser light L converge is a theoretical laserlight-converging point, and thus has such a high optical intensity thata minute structural change occurs, thereby forming the minute void 14whose surroundings do not change in terms of the crystal structure,whereas the part formed with the molten processed region 13 is thermallyaffected so much as to be simply melted and then re-solidified.

Here, the molten processed region is as stated in (1) mentioned above,whereas the minute void is one whose surroundings do not change in termsof the crystal structure. When the semiconductor substrate has a siliconmonocrystal structure, the surroundings of the minute void are likely tokeep the silicon monocrystal structure.

By an experiment, the inventors have verified that molten processedregions and minute voids are formed within a silicon wafer which is anexample of the semiconductor substrate. Conditions for the experimentare as follows:

(A) Object to be processed: silicon wafer (having a thickness of 100 μm)

(B) Laser

-   -   Light source: semiconductor laser pumping Nd:YAG laser    -   Wavelength: 1064 nm    -   Repetition frequency: 40 kHz    -   Pulse width: 30 nsec    -   Pulse pitch: 7 μm    -   Processing depth: 8 μm    -   Pulse energy: 50 μJ/pulse

(C) Light-converging lens

-   -   N. A.: 0.55

(D) Moving speed of a mounting table mounting the object: 280 mm/sec

FIG. 11 is a view showing photographs of a cut section of a siliconwafer cut by laser processing under the above-mentioned conditions. InFIGS. 11, (a) and (b) are photographs showing the same cut section inrespective scales different from each other. As depicted, pairs ofmolten processed regions 13 and minute voids 14, each pair being formedupon irradiation with one pulse of laser light L, are made with apredetermined pitch along the cut section (i.e., along a line alongwhich the substrate should be cut). Each of the molten processed regions13 of the cut section shown in FIG. 11 has a width of about 13 μm in thethickness direction of the silicon wafer 11 (the vertical direction inthe drawing) and a width of about 3 μm in the direction of moving thelaser light L (the horizontal direction in the drawing). Each of theminute voids 14 has a width of about 7 μm in the thickness direction ofthe silicon wafer 11 and a width of about 1.3 μm in the direction ofmoving the laser light L. The gap between each molten processed region13 and its corresponding minute void 14 is about 1.2 μm.

The cases of (1) and (2) are explained in the foregoing as a modifiedregion formed by multiphoton absorption. When a starting point regionfor cutting is formed as follows in view of the crystal structure of thesemiconductor substrate, its cleavage property, and the like, thesemiconductor substrate can be cut accurately with a smaller force fromthe starting point region for cutting acting as a start point.

Namely, in the case of a substrate made of a monocrystal semiconductorhaving a diamond structure such as silicon, the starting point regionfor cutting is preferably formed in a direction along the (111) plane(first cleavage plane) or (110) plane (second cleavage plane). In thecase of a substrate made of a III-V family compound semiconductor havinga zinc ore type structure such as GaAs, the starting point region forcutting is preferably formed in a direction along the (110) plane.

When the substrate is formed with an orientation flat along a directionto be formed with the starting point region for cutting (e.g., in adirection along the (111) plane in the monocrystal silicon substrate) ora direction orthogonal to the direction to be formed with the startingpoint region for cutting, the starting point region for cuttingextending along the direction to be formed with the starting pointregion for cutting can be formed in the substrate in an easy andaccurate manner with reference to the orientation flat.

A preferred embodiment of the semiconductor substrate cutting method inaccordance with the present invention will now be explained morespecifically. FIGS. 13 to 16 are partial sectional views of the siliconwafer taken along the line XIII-XIII of FIG. 12.

As shown in FIG. 12, on the front face 3 of the silicon wafer(semiconductor substrate) 11 to become an object to be processed, aplurality of functional devices 15 are formed into a matrix pattern indirections parallel and perpendicular to the orientation flat 16. In thefollowing manner, such a silicon wafer 11 is cut into the individualfunctional devices 15.

First, as shown in FIG. 13(a), a protective film 18 is attached to thefront face 3 side of the silicon wafer 11, so as to cover the functionaldevices 15. The protective film 18 protects the functional devices 15and hold the silicon wafer 11. After attaching the protective film 18,as shown in FIG. 13(b), the rear face 17 of the silicon wafer 11 issubjected to surface grinding such that the silicon wafer 11 attains apredetermined thickness, and then is subjected to chemical etching so asto be smoothed. Thus, for example, the silicon wafer 11 having athickness of 350 μm is thinned to a thickness of 100 μm. After thesilicon wafer 11 is thinned, the protective film 18 is irradiated withUV rays. This hardens a UV-curable resin layer which is an adhesivelayer of the protective film 18, thereby making the protective film 18easier to peel off from the silicon wafer 11.

Subsequently, using a laser processing apparatus, a starting pointregion for cutting is formed within the silicon wafer 11. Namely, asshown in FIG. 14(a), the protective film 18 is secured by vacuum suctiononto a mounting table 19 of the laser processing apparatus such that therear face 17 of the silicon wafer 11 faces up, and a line along whichthe substrate should be cut 5 is set like a grid (see dash-double-dotlines in FIG. 12) running between neighboring functional devices 15, 15.Then, as shown in FIG. 14(b), the silicon wafer 11 is irradiated withlaser light L under the above-mentioned condition generating multiphotonabsorption while positioning a light-converging point P within thesilicon wafer 11 with the rear face 17 acting as a laser light incidentface, and the mounting table 19 is moved such that the light-convergingpoint P is relatively moved along the line along which the substrateshould be cut 5. Consequently, as shown in FIG. 14(c), molten processedregions 13 form starting point regions for cutting 8 within the siliconwafer 11 along the line along which the substrate should be cut 5.

Subsequently, the silicon wafer 11 having the protective film 18attached thereto is removed from the mounting table 19, and a diebonding resin bearing film 20 (e.g., LE-5000 (product name) by LintecCorporation) is attached to the rear face 17 of the silicon wafer 11 asshown in FIG. 15(a). The die bonding resin bearing film 20 comprises anexpandable expansion film (holding member) 21 having a thickness ofabout 100 μm. On the expansion film 21, a die bonding resin layer (anadhesive resin layer) 23 functioning as a die bonding adhesive isdisposed by way of a UV-curable resin layer having a thickness ofseveral μm. Namely, the expansion film 21 is attached to the rear face17 of the silicon wafer 11 by way of the die bonding resin layer 23.Film expanding means 30 are attached to marginal parts of the expansionfilm 21. After attaching the die bonding resin bearing film 20, theprotective film 18 is peeled off from the front face 3 side of thesilicon wafer 11 as shown in FIG. 15(b), and the expansion film 21 isirradiated with UV rays as shown in FIG. 15(c). This hardens aUV-curable resin layer which is an adhesive layer of the expansion film21, thereby making the die bonding resin layer 23 easier to peel offfrom the expansion film 21.

Subsequently, as shown in FIG. 16(a), the film expanding means 21 pullthe marginal parts of the expansion film 21 outward, thereby expandingthe expansion film 21. Expanding the expansion film 21 generatesfractures from the starting point regions for cutting 8 acting as startpoints, and these fractures reach the front face 3 and rear face 17 ofthe silicon wafer 11. As a consequence, the silicon wafer 11 is cutaccurately along the line along which the substrate should be cut 5,whereby a plurality of semiconductor chips 25 each having one functionaldevice 15 are obtained. Here, as the expansion film 21 expands, opposingcut surfaces 25 a, 25 a of neighboring semiconductor chips 25, 25 arereleased from their close contact state. Therefore, simultaneously withthe cutting of the silicon wafer 11, the die bonding resin layer 23closely in contact with the rear face 17 of the silicon wafer 11 is cutalong the line along which the substrate should be cut 5.

Then, as shown in FIG. 16(b), the semiconductor chips 25 aresuccessively picked up by a suction collect or the like. Here, the diebonding resin layer 23 is cut into an outer shape equivalent to that ofthe semiconductor chip 25, whereas the adhesion force between the diebonding resin layer 23 and the expansion film 21 is lowered, whereby thesemiconductor chip 25 is picked up while in a state where the cut pieceof the die bonding resin layer 23 is in lose contact with the rear facethereof. Then, as shown in FIG. 16(c), the semiconductor chip 25 ismounted by way of the die bonding resin layer 23 in close contact withthe rear face thereof onto a die pad of a lead frame 27, and is bondedto the latter with the filler upon heating.

In the method of cutting the silicon wafer 11 in the foregoing, thesilicon wafer 11 having the front face 3 formed with the functionaldevices 15 is employed as an object to be processed, and the siliconwafer 11 is irradiated with the laser light L while positioning thelight-converging point P within the silicon wafer 11 with the rear face17 acting as a laser light incident face. This generates multiphotonabsorption within the silicon wafer 11, thereby causing the moltenprocessed region 13 to form the starting point region for cutting 8within the silicon wafer 11 along the line along which the substrateshould be cut 5. Here, the rear face of the semiconductor substrate isemployed as the laser light incident face, since there is a fear of thefunctional device restraining laser light from entering when the frontface is used as the laser light incident face. When the starting pointregion for cutting 8 is formed within the silicon wafer 11 as such, afracture can be generated from the starting point region for cutting 8acting as a start point naturally or with a relatively small forceapplied thereto, so as to reach the front face 3 and rear face 17 of thesilicon wafer 11. Therefore, after the starting point region for cutting8 is formed, the expandable holding member 21 is attached to the rearface 17 of the silicon wafer 11 by way of the die bonding resin layer23, whereby the cut surfaces 25 a, 25 a of the semiconductor substratecut along the line along which the substrate should be cut 5 arereleased from their close contact state as the expansion film 21expands. This also cuts the die bonding resin layer 23 existing betweenthe silicon wafer 11 and expansion film 21 along the line along whichthe substrate should be cut 5. Hence, the silicon wafer 11 and diebonding resin layer 23 can be cut along the line along which thesubstrate should be cut 5 much more efficiently than in the case cutwith a blade.

Also, since, the cut surfaces 25 a, 25 a of the silicon wafer 11 cutalong the line along which the substrate should be cut 5 are initiallyin close contact with each other, the cut individual pieces of thesilicon wafer 11 and the cut individual pieces of the die bonding resinlayer 23 have substantially the same outer shape, whereby the diebonding resin can be prevented from protruding from the cut surface 25of each piece of the silicon wafer 11.

Further, before forming the starting point region for cutting 8 withinthe silicon wafer 11, the rear face 17 of the silicon wafer 11 is groundsuch that the silicon wafer 11 attains a predetermined thickness. Whenthe silicon wafer 11 is thinned to a predetermined thickness as such,the silicon wafer 11 and die bonding resin 23 can be cut more accuratelyalong the line along which the substrate should be cut 5.

The above-mentioned method of cutting the silicon wafer 11 relates to acase where, as shown in FIG. 17(a), no fracture generated from thestarting point region for cutting 8 acting as a start point occurs inthe silicon wafer 11 until the expansion film 21 is expanded. However,as shown in FIG. 17(b), a fracture 28 may be generated from the startingpoint region for cutting 8 acting as a start point and caused to reachthe front face 3 and rear face 17 of the silicon wafer 11 beforeexpanding the expansion film 21. Examples of the method of generatingthe fracture 28 include one in which stress applying means such as aknife edge is pressed against the rear face 17 of the silicon wafer 11along the starting point region for cutting 8, so as to generate abending stress or shearing stress in the silicon wafer 11 along thestarting point region for cutting 8; and one in which a temperaturedifference is imparted to the silicon wafer 11, so as to generate athermal stress in the silicon wafer 11 along the starting point regionfor cutting 8.

Stressing and cutting the silicon wafer 11 along the starting pointregion for cutting 8 as such before expanding the expansion film 21 canyield a semiconductor chip 25 which is cut with a very high accuracy.When the expansion film 21 attached to the silicon wafer 11 is expanded,the opposing cut surfaces 25 a, 25 a of the neighboring semiconductorchips 25, 25 are released from their close contact state in this case aswell, whereby the die bonding resin layer 23 closely in contact with therear face 17 of the silicon wafer 11 is cut along the cut surfaces 25 a.Therefore, the silicon wafer 11 and die bonding resin layer 23 can becut along the starting point region for cutting 8 much more efficientlyin this cutting method than in the case of cutting with a blade.

When the silicon wafer 11 is thin, the fracture 28 generated from thestarting point region for cutting 8 acting as a start region may reachthe front face 3 and rear face 17 of the silicon wafer 11 as shown inFIG. 17(b) even if no stress is generated along the starting pointregion for cutting 8.

When the starting point region for cutting 8 due to the molten processedregion 13 is formed within the silicon wafer 11 near the front face 3,and the fracture 28 is allowed to reach the front face 3 as shown inFIG. 18(a), the cutting accuracy can be made very high in the front face(i.e., the surface formed with the functional device) of thesemiconductor chip 25 obtained by cutting. When the starting pointregion for cutting 8 due to the molten processed region 13 is formedwithin the silicon wafer 11 near the rear face 17, and the fracture 28is allowed to reach the rear face 17 as shown in FIG. 18(b), on theother hand, the die bonding resin layer 23 can be cut accurately byexpanding the expansion film 21.

The present invention is not limited to the above-mentioned embodiment.For example, though the above-mentioned embodiment relates to a casewhere the modified region 7 is formed by generating multiphotonabsorption within the semiconductor substrate 1, there are cases wherethe modified region 7 can be formed by generating optical absorptionequivalent to multiphoton absorption within the semiconductor substrate1.

Though the above-mentioned method of cutting the silicon wafer 11relates to a case where the molten processed region 13 is formed as amodified region, the molten processed region 13 and minute void 14 maybe formed as a modified region. In this case, since the rear face 17 ofthe silicon wafer 11 is employed as the laser light incident face, theminute void 14 is formed on the opposite side of the molten processedregion 13 from the laser light incident face, i.e., the front face 3side formed with the functional device 15. In cut surfaces, the part onthe minute void 14 side tends to attain an accuracy higher than that inthe part on the molten processed region 13 side, whereby the yield ofthe semiconductor chips 25 can further be improved when the minute void14 is formed on the front face 3 side formed with the functional device15.

If the die bonding resin layer 23 is heated before expanding theexpansion film 21 of the die bonding resin bearing film 20, the diebonding resin layer 23 can be cut more accurately and easily along theline along which the substrate should be cut 5 simultaneously with thecutting of the silicon wafer 11 when expanding the expansion film 21.This seems to be because the die bonding resin layer 23 changes itsphysical property to one easy to tear apart upon heating. Specifically,when the die bonding resin layer 23 is heated for 1 to 30 minutes at atemperature of 50° C. to 120° C., the die bonding resin layer 23 changesits physical property to one easy to tear apart upon heating. In thisregard, the die bonding resin layer 23 is less likely to change itsphysical property when the temperature is lower than 50° C., whereasthere is a fear of the die bonding resin layer 23 softening such as tolose its original shape if the temperature exceeds 120° C.

As a method of heating the die bonding resin layer 23 as mentionedabove, the die bonding resin layer 23 as a whole may be heated, or apart of the die bonding resin layer 23 along the line along which thesubstrate should be cut 5 may selectively be heated. For heating the diebonding resin layer 23 as a whole, the silicon wafer 11 and the diebonding resin bearing film 20 attached to the rear face 17 of thesilicon wafer 11 may be blown by warm air, put into a heating furnace,or mounted on a heating table in which a heater is embedded. Forselectively heating a part of the die bonding resin layer 23 along theline along which the substrate should be cut 5, it will be sufficient ifthe line along which the substrate should be cut 5 is irradiated withlaser light to which the die bonding resin layer 23 exhibits opticalabsorption, etc.

The die bonding resin layer 23 may be heated at any time from when theexpansion film 21 is attached to the rear face 17 of the silicon wafer11 by way of the die bonding resin layer 23 until the silicon wafer 11and die bonding resin layer 23 are cut along the line along which thesubstrate should be cut 5 by expanding the expansion film 21. Beforeattaching the expansion film 21 to the rear face 17 of the silicon wafer11 by way of the die bonding resin layer 23, the die bonding resin layer23 may be heated while in the state of the die bonding resin bearingfilm 20, and then the expansion film 21 may be attached to the siliconwafer 11 by way of thus heated die bonding resin layer 23. In this case,the expansion film 21 may be attached to the silicon wafer 11 by way ofthe heated die bonding resin layer 23 immediately after heating the diebonding resin layer 23, or after a predetermined time from the heatingof the die bonding resin layer 23. One of reasons why heating makes thedie bonding resin layer 23 easier to divide as such seems to lie in thatit reduces fracture elongation and increases tensile strength. Also,there are cases where the die bonding resin layer 23 can change itsphysical property to one easy to tear apart when irradiated withelectromagnetic waves such as UV rays.

Here, specific examples of selectively heating the part of die bondingresin layer 23 along the line along which the substrate should be cut 5will be explained. Among the drawings, parts identical or equivalent toeach other will be referred to with numerals identical to each otherwithout repeating their overlapping descriptions.

First, as shown in FIG. 19(a), a protective film 18 is attached to thefront face 3 side of the silicon wafer 11, so as to cover the functionaldevices 15, and then is secured by vacuum suction onto the mountingtable 19 of the laser processing apparatus such that the rear face 17 ofthe silicon wafer 11 faces up. After a line along which the substrateshould be cut 5 is set like a grid running between neighboringfunctional devices 15, 15, the silicon wafer 11 is irradiated with laserlight L under the condition generating multiphoton absorption whilepositioning a light-converging point P within the silicon wafer 11 withthe rear face 17 acting as a laser light incident face as shown in FIG.19(b), and the mounting table 19 is moved such that the light-convergingpoint P is relatively moved along the line along which the substrateshould be cut 5. Consequently, as shown in FIG. 19(c), molten processedregions 13 form starting point regions for cutting 8 within the siliconwafer 11 along the line along which the substrate should be cut 5. Inplace of the protective film 18, a plate-like protective member made ofglass or a resin may be attached to the front face 3 side of the siliconwafer 11.

Subsequently, as shown in FIG. 20(a), a die bonding resin layer 23 issecured to the rear face 17 of the silicon wafer 11, and the protectivefilm 18 is secured by vacuum suction onto the mounting table 19 of thelaser processing apparatus such that the rear face 17 of the siliconwafer 11 faces up. Then, as shown in FIG. 20(b), the die bonding resinlayer 23 is irradiated with laser light L having a predeterminedwavelength (e.g., 808 nm) while positioning a light-converging point Ptherewithin, and the mounting table 19 is moved such that thelight-converging point P is relatively moved along the line along whichthe substrate should be cut 5. Consequently, as shown in FIG. 20(c), amodified region 29 having such a property that it is easy to tear apartis formed in the die bonding resin layer 23 along the line along whichthe substrate should be cut 5. This modified region 29 is one having aphysical property changed or weakened by a heating effect. The diebonding resin layer 23 may be irradiated along the line along which thesubstrate should be cut 5 with electron beams instead of the laser lightL having a predetermined wavelength.

Subsequently, the silicon wafer 11 is removed from the mounting table 19and, as shown in FIG. 21(a), an expansion film 21 is attached by way ofan adhesive layer (an adhesive whose adhesion force weakens uponirradiation with UV rays and other energy beams) 31 to the die bondingresin layer 23 secured to the silicon wafer 11. The expansion film 21with the adhesive layer 31 may be attached to the die bonding resinlayer 23, or the expansion film 21 may be attached to the die bondingresin layer 23 after the adhesive layer 31 is laminated thereon.

Then, the protective film 18 is peeled off from the front face 3 side ofthe silicon wafer 11 as shown in FIG. 21(b), and marginal parts of theexpansion film 21 are pulled outward as shown in FIG. 21(c), so as toexpand the expansion film 21. As the expansion film 21 is expanded, afracture occurs in the thickness direction from the starting pointregion for cutting 8 acting as a start region, and reaches the frontface 3 and rear face 17 of the silicon wafer 11. This cuts the siliconwafer 11 accurately along the line along which the substrate should becut 5, thereby yielding a plurality of semiconductor chips 25 eachhaving one functional device 15. Here, opposing cut surfaces 25 a, 25 aof neighboring semiconductor chips 25, 25 are released from their closecontact state as the expansion film 21 expands, whereby the die bondingresin layer 23 closely in contact with the rear face 17 of the siliconwafer 11 is cut along the line along which the substrate should be cut 5simultaneously with the cutting of the silicon wafer 11.

Subsequently, the adhesive layer 31 is irradiated with UV rays or otherenergy beams, so as to lower its adhesion force, and the semiconductorchips 25 with their corresponding cut pieces of the die bonding resinlayer 23 closely in contact therewith are successively picked up.

Another specific example of selectively heating the part of die bondingresin layer 23 along the line along which the substrate should be cut 5will now be explained. Among the drawings, parts identical or equivalentto each other will be referred to with numerals identical to each otherwithout repeating their overlapping descriptions.

First, as in the specific example mentioned above, molten processedregions 13 form starting point regions for cutting 8 within the siliconwafer 11 along a line along which the substrate should be cut 5.Thereafter, as shown in FIG. 22(a), a die bonding resin bearing film 32is attached to the rear face 17 of the silicon wafer 11, and theprotective film 18 is secured by vacuum suction onto the mounting table19 of the laser processing apparatus such that the rear face 17 of thesilicon wafer 11 faces up. The die bonding resin bearing film 32 is onein which a die bonding resin layer 23 is disposed by way of an adhesivelayer 31 on an expansion film 21 which is made of a materialtransmitting laser light L having a predetermined wavelength (e.g., 808nm). As the die bonding resin bearing film 32, one in which the diebonding resin layer 23 is directly disposed on the expansion film 21made of a material transmitting laser light L having a predeterminedwavelength may be used as well (see, for example, Japanese PatentPublication No. 1987034).

After being attached, the die bonding resin bearing film 32 isirradiated with the laser light L while positioning a light-convergingpoint P within the die bonding resin layer 23 as shown in FIG. 22(b),and the mounting table 19 is moved such that the light-converging pointP is relatively moved along the line along which the substrate should becut 5. Consequently, as shown in FIG. 22(c), a modified region 29 havingsuch a property that it is easy to tear apart is formed in the diebonding resin layer 23 along the line along which the substrate shouldbe cut 5.

Subsequently, the protective film 18 is peeled off from the front face 3side of the silicon wafer 11 as shown in FIGS. 23(a) and (b), andmarginal parts of the expansion film 21 are pulled outward as shown inFIG. 23(c), so as to expand the expansion film 21. As the expansion film21 is expanded, a fracture occurs in the thickness direction from thestarting point region for cutting 8 acting as a start region, andreaches the front face 3 and rear face 17 of the silicon wafer 11. Thiscuts the silicon wafer 11 accurately along the line along which thesubstrate should be cut 5, thereby yielding a plurality of semiconductorchips 25 each having one functional device 15. Here, opposing cutsurfaces 25 a, 25 a of neighboring semiconductor chips 25, 25 arereleased from their close contact state as the expansion film 21expands, whereby the die bonding resin layer 23 closely in contact withthe rear face 17 of the silicon wafer 11 is cut along the line alongwhich the substrate should be cut 5 simultaneously with the cutting ofthe silicon wafer 11.

Subsequently, the adhesive layer 31 is irradiated with UV rays or otherenergy beams, so as to lower its adhesion force, and the semiconductorchips 25 with their corresponding cut pieces of the die bonding resinlayer 23 closely in contact therewith are successively picked up. Theadhesive layer 31 may be irradiated with UV rays or other energy beamseither before or after expanding the expansion film 21.

Though the die bonding resin layer 23 is irradiated with laser lighthaving a predetermined wavelength along the line along which thesubstrate should be cut 5 in each of the above-mentioned specificexamples, a mask formed with a light-transmitting part along the linealong which the substrate should be cut 5 may be disposed on the diebonding resin layer 23 or die bonding resin bearing film 32, and totallyirradiated with UV rays or other energy beams, so as to form a modifiedregion 29 in the die bonding resin layer 23 along the line along whichthe substrate should be cut 5.

INDUSTRIAL APPLICABILITY

In the present invention, as explained in the foregoing, a semiconductorsubstrate having a front face formed with a functional device canefficiently be cut together with a die bonding resin layer.

1-8. (canceled)
 9. A semiconductor substrate cutting method for cuttinga semiconductor substrate having a front face formed with a plurality offunctional devices into the individual functional devices, so as tomanufacture a semiconductor device having the functional device, themethod comprising the steps of: attaching a protective member to thefront face of the semiconductor substrate, such that the functionaldevices are covered; irradiating the semiconductor substrate with laserlight while positioning a light-converging point within thesemiconductor substrate with a rear face of the semiconductor substrateacting as a laser light incident face after the step of attaching theprotective member, so as to form a modified region, and causing themodified region to form a starting point region for cutting along eachline along which the semiconductor substrate should be cut, the linesset like a grid running between the neighboring functional devices,inside by a predetermined distance from the laser light incident face;attaching an expandable holding member to the rear face of thesemiconductor substrate by way of a die bonding resin layer afterforming the starting point regions for cutting; cutting thesemiconductor substrate and the die bonding resin layer from thestarting point regions for cutting along each of the lines in the gridby expanding the holding member after attaching the holding member, soas to obtain a plurality of semiconductor chips each having a front faceformed with the functional device and having a cut piece of the diebonding resin layer in close contact with a rear face thereof; andmounting the semiconductor chip onto a support body by way of the cutpiece of the die bonding resin layer in close contact with the rear facethereof, so as to obtain the semiconductor device.
 10. A semiconductorsubstrate cutting method according to claim 9, wherein the support bodyis a lead frame.
 11. A semiconductor substrate cutting method accordingto claim 9, wherein the holding member is expanded after the protectivemember is removed from the front face of the semiconductor substrate.